The long term objective of this continuing research is to achieve accurate tumor dosimetry from external imaging. A focus is to establish a strong relationship between res- ponse and dosimetric variables. The investigators seek to establish cost effective treatment of patients with non-Hodgkin s lymphoma by administration of a combination regimen of non-radioactive plus I-131 labelled anti-B1 monoclonal antibody. A primary goal is to be able to select patients appropriately for this non- marrow-ablative therapy. The three specific aims are: (1) to analyze and refine the existing protocol for measuring tumor dosimetry, (2) to apply the protocol to non-Hodgkin s lymphoma patients who are being treated with the combined anti-B1 therapy for determination of the relationships between dosimetric variables and response of both the patient as a whole and of individual tumors, and (3) to establish a method to predict outcome of therapy from tracer studies.